The present invention relates to the field of products for treating contact lenses. More specifically, the invention relates to improved saline solutions for rinsing, soaking and storing contact lenses. The saline solutions of the present invention are believed to represent a significant improvement over prior saline solutions utilized for similar purposes, because the present solutions do not contain conventional antimicrobial preservatives which have been frequently associated with various toxic effects on ophthalmic tissues. Prior saline solutions have been either preserved or unpreserved. The antimicrobial agents utilized in the preserved salines have principally been sorbic acid or thimerosal, although polymeric antimicrobial agents have also been utilized. Salines which are preserved with sorbic acid or thimerosal are known to discolor lenses, and thimerosal is known to cause hypersensitivity reactions in some patients. These prior saline solutions are also incompatible with oxidizing agents, such as chlorine, hypochlorous acid and iodine.
Ethylenediaminetetraacetic acid and the monosodium, disodium and trisodium salts thereof (collectively referred to herein as "EDTA") have been widely used for many years in ophthalmic products, particularly products for treating contact lenses, such as saline solutions. EDTA has been utilized in preserved saline solutions to enhance the antimicrobial efficacy of the above-mentioned chemical preservatives, particularly the efficacy of those preservatives against gram negative bacteria. However, some scientific studies have indicated that EDTA may damage corneal cells. See, e.g., Collin, et al., "The Effects of Na.sub.2 EDTA on Keratocytes and Endothelium of the Isolated Guinea Pig Cornea", International Contact Lens Clinic, volume 9, number 5, September/October 1982. Further, it is also incompatible with certain components of compositions for treating contact lenses, such as chlorine, iodine and other oxidizing agents.
Unpreserved saline solutions marketed in multi-dose containers are either packaged in aerosol containers or squeczablc plastic bottles. Saline solutions packaged in aerosol cans are expensive due to the cost of containers and specialized technology. Moreover, saline solutions contained in aerosol cans are Gamma irradiated to achieve sterility; this produces peroxides in the solutions. These peroxides react with chlorine or hypochlorous acid to form microbiologically inactive chloride. Consequently, aerosol salines are not compatible with contact lens disinfecting systems which use oxidizing agents such as chlorine, hypochlorous acid or iodine. Unpreserved salines may also be packaged in squeezable bottles; however, these solutions have poor antimicrobial activity and must be discarded after 30 days of use once the container is opened.
In 1990, a second generation saline solution which eliminated some of the disadvantages of the first generation saline solutions was introduced. However, this saline solution, which contains fifty pans per million of metaborate as a preservative, may cause corneat damage upon long-term use. Moreover, peroxide-preserved saline solutions are not compatible with oxidizing agents like chlorine. This incompatibility precludes the use of peroxide-preserved saline solutions as diluents for contact lens disinfecting tablets containing chlorine or other oxidizing agents.
In view of the foregoing circumstances, there is a need for improved saline solutions for treating contact lenses which are: (1) adequately preserved to prevent any risk of antimicrobial contamination of the solution or contact lenses treated with the solution, (2) nontoxic to ophthalmic tissues and (3) chemically compatible with oxidizing agents. There is particularly a need for a preserved, multidose saline solution which meets the foregoing requirements and does not contain EDTA. The present invention is directed to satisfying these needs.